It is known that solid catalyst components having organic magnesium compounds, either directly or after having been subjected to an activating treatment, held in contact with transition metal compounds have been proposed for use in the polymerization of olefins. For example, solid catalyst components produced by using dialkyl magnesium as organic magnesium compounds, holding these dialkyl magnesium, either independently or in the form of complexes thereof with alkyl metals such as trialkyl aluminum, in contact with alcohols, and causing the resultant reaction products to be held in contact with titanium compounds have been proposed (specifications of Japanese Patent Application Laid-open SHO No. 53[1978]-87,990 and SHO-54[1979]-57,491).
These solid catalyst components, however, can hardly be called satisfactory in terms of catalytic activity. Particularly for the polymerization of alpha-olefins such as propylene, they fall short of being feasible because of inferior stereoregularity.